Anmol Baranwal writes a comprehensive guide to AG-UI, an open protocol that standardizes how agents communicate with user-facing applications by replacing custom streaming layers with a unified event stream. The protocol connects agentic backends to frontends across any framework and surface, defining 31 event types grouped into 8 categories covering runs, text, tool calls, reasoning, state, activity, subagents, and custom events. It operates alongside MCP (agent-to-tool) and A2A (agent-to-agent) as the user-facing layer, and its 1.0 specification is stable, backwards compatible, and backed by major tech companies.
- Google, Microsoft, Amazon, and Oracle have adopted the protocol
- SDKs for TypeScript, Python, and .NET are generated from a shared JSON Schema, with community SDKs for Go, Ruby, Rust, Dart, Kotlin, Java, and C++
- Transport-agnostic design supports HTTP SSE, WebSockets, and Protobuf binary format
- AG-UI 1.0 adds subagent support, multimodal tool results, human-in-the-loop interrupts, and token usage tracking
- CopilotKit Intelligence uses captured interaction data with Automatic Learning to extract insights and generate Skills that improve agent behavior over time